This application is based on Japanese Patent Application No. 2003-29492 filed on Feb. 6, 2003, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention is related to an air intake system of an internal combustion engine.
2. Description of Related Art
In a conventional air intake system described in JP-A10-103089, a throttle body for supporting a throttle valve is inserted into an intermediate section within the intake pipe in an axial direction of the intake pipe. The throttle valve opens and closes an air intake passage which is formed by the throttle body and the intake pipe.
In the above air intake system, when moisture generated due to condensation of the intake gas sticks to the throttle valve, the throttle valve may be frozen to be immovable when the temperature is low. Therefore, a heating system or the like is provided for heating the throttle valve so that the throttle valve is prevented from being frozen.
When the heating system is provided for heating the throttle valve, significant increase of a production cost is inevitable. Therefore, an air intake system may be considered such that a flow blocking member is integrally provided with a throttle body in a bore, so that moisture is blocked from flowing to the throttle valve. However, in this case, an extra member such as the flow blocking member is provided in the throttle body. Thus, the throttle body deforms when the flow blocking member is integrally formed with the throttle body, and dimensional accuracy of the bore is apt to decrease. When the dimensional accuracy of the bore decreases, tolerance of a clearance formed between the inner wall surface of the bore, which defines an air intake passage, and the outer peripheral section of the throttle valve increases.
In view of the foregoing problems, it is an object of the present invention to provide an air intake system, in which a specific fluid is restricted from reaching the throttle valve while a dimensional accuracy of the throttle valve is secured. The other object of the present invention is to provide an air intake system which can decrease a production cost.
According to the present invention, an air intake system includes an intake pipe, a throttle body, a throttle valve and a flow blocking member. The intake pipe has an upstream end and a downstream end. The throttle body is inserted into the intake pipe at a section between the upstream end and the downstream end in an axial direction of the intake pipe, so as to define an intake passage with the intake pipe through which intake gas flows. The throttle valve opens and closes the intake passage, and is supported in the throttle body. In the air intake system, the flow blocking member is integrally formed with the intake pipe for blocking a flow of a specific fluid toward the throttle valve in the intake passage. Accordingly, an extra member, such as the flow blocking member, need not to be provided to the throttle body. Thus, a forming deformation of the throttle body is prevented and a dimensional accuracy of the throttle body can be secured. Furthermore, because the flow blocking member is integrally formed with the intake pipe, an increase of a production cost due to adding the flow blocking member can be prevented.
Preferably, the flow blocking member is arranged at an upstream side with respect to the throttle valve in the intake passage, and the specific fluid is a condensate of the intake gas passing through the intake passage. In this case, the condensate can be effectively collected around the flow blocking member, and it can effectively prevent the condensate from being introduced into the throttle valve by the flow blocking member.
Specifically, the flow blocking member forms an inlet port which opens to an upstream side in the intake passage, and the inlet port is provided in such a manner that the condensate is introduced into the inlet port from an upstream side with respect to the throttle valve in the intake passage. Further, the flow blocking member includes an inner-pipe section that is arranged in an inner peripheral side of the intake pipe substantially in parallel in axial so as to form the inlet port between the intake pipe and the inner-pipe section, and a blocking section that closes between the intake pipe and the inner-pipe section on a downstream side with respect to the inlet port of the intake passage.
Preferably, the flow blocking member is arranged at a downstream side with respect to the throttle valve in the intake passage, and the specific fluid is exhaust gas exhausted from an internal combustion engine and introduced into the intake passage. In this case, a flow of exhaust gas toward the throttle valve is blocked by the flow blocking member. In this case, the intake pipe has an introduction port for introducing the exhaust gas to a downstream side with respect to the throttle valve in the intake passage. The flow blocking member forms an outlet port, which opens to a downstream side in the intake passage, on a downstream side with respect to the introduction port of the intake passage. Further, the flow blocking member is provided to guide the exhaust gas, which is introduced into the introduction port, to a downstream side through the outlet port. Specifically, the flow blocking member includes an inner-pipe section that is arranged in an inner peripheral side of the intake pipe substantially in parallel in axial so as to form the outlet port between the intake pipe and the inner-pipe section, and a blocking section that closes between the intake pipe and the inner-pipe section on an upstream side with respect to the introduction port of the intake passage.